Seasonal and social correlates of changes in hair, skin, and scrotal condition in vervet monkeys (Cercopithecus aethiops) of Amboseli National Park, Kenya

In a 20-month study of six groups of vervet monkeys (Cercopithecus aethiops) in Amboseli National Park, Kenya, I documented changes in hair loss in all individuals, and scrotal color and hyperpigmentation in all adult males. Hair loss occurred seasonally and was most pronounced in low-ranking individuals, especially males. The mean shade of scrotal color for all males and the percentage of males with scrotal hyperpigmentation both covaried with hair loss over time. Scrotal color was strongly negatively correlated with scrotal hyperpigmentation. The underlying causes are not yet known. I present three scenarios based on nutrition, stress from competition, or a combination of the two, that might explain these patterns. Awareness of these easily observable changes may provide field-workers with a quickly assessed visual measure of physical or emotional stress in free-ranging vervets.